The contour grinding of unfired "green" ceramic spark plug insulators is one of the critical steps of the spark plug manufacturing process. Excessive grinding forces during this stage result in reduced yields due to part breakage and/or cracking. Many parameters affect grinding. These factors include: the blank size and shape, the blank forming pressure, the control means speed and condition, the durometer of the control wheel tire, grinding wheel type and condition, etc. In order to optimize the grinding process and therefore to increase yields and throughput, instrumentation for measuring the forces that occur during grinding is desirable. Such instrumentation can also be used to optimize the machine setup, to determine process trends, and as a tool in the development of new designs and materials. Additionally, closed loop control circuits can be incorporated on the grinders, such that the process controller would automatically monitor the operation and shut it down if the grinding forces exceeded preset limits or make corrective adjustments.
As evidenced by the U.S. Pat. No. 2,091,973 to Fessler et al it has long been known grind the unfired spark plug insulator by rotatably supporting it on a spindle, rotate the insulator by a driving wheel applied to the outer surface of the insulator, and applying a shaped grinding wheel to the insulator in opposition to the driving wheel. Although the grinding equipment has been much improved and automated since the time of that patent, the same basic support, driving and grinding forces are employed and the equipment has not, prior to this invention, incorporated means for measuring the forces. Even when major grinding equipment changes are contemplated, the desirability of measuring the forces on the part remains. The need for such measurement is in no way limited to spark plug manufacture since other ceramic parts such as bushings or oxygen sensors undergo grinding and have similar hazards to be avoided or benefits to be gained during their manufacture.